The present invention relates to a double-side printing apparatus and its control method which are applied to a page printer equipped with a double-side printing mechanism such as a laser printer, an LCD (Liquid Crystal Diode) printer, an LCS (Liquid Crystal Shutter) printer.
In recent years, double-side printing has been coming into wide use. Double-side printing is the printing of data of different pages on the right and reverse-side of a sheet. Japanese Patent Laid-open No. HEI 1-160731, HEI 4-1067 and HEI 4-7174 disclose controllers for page printers with a double-side printing mechanisms. However, In these apparatuses, sizes of a right-side page and a reverse-side page which is printed on a sheet must be the same size. On the other hand, Japanese Patent laid-open No. 2-63870 discloses a printer that prints data of a plurality of pages on each of the right and reverse sides of sheets.
In such apparatuses, printing operation stops or causes an error due to a mixture of different sheets in the printer if the sizes are different between the right-side page and the reverse-side page to be printed on a sheet. That is, the conventional apparatus cannot handle print data that indicate different sizes between the right-side page and the reverse-side page to be printed on a sheet. The print data are also called document data and includes a series of print commands. In other words, an user must always be concerned about the sizes of the pages between the right-side and the reverse-side.
Also, when the printing controller receives the document data of only one document and the document data is ended with only a right or reverse side page, more than one printed pages including the last page are kept in the printer until the printing control apparatus receives the next document data because the last page is not clearly indicated by the document data. That is, a user cannot obtain the complete sheets of the document until the next document data has been received. Also some kinds of printers indicate "printer error" message (such as a paper-jam message) due to their mechanism when a sheet has been kept in the printer for a period of time.
In addition, since the above described conventional technology has been developed not for circulation-type double-side printing mechanisms but intermediate tray-type double-side printing mechanisms, double-side printing control with freedom equal to or higher than the conventional technology cannot be implemented. The following items are not taken into account:
(1) A function that allows changes of a paper size and the number of copies in one document or for each page.
(2) A processing specification and a processing procedure for handling double-side printing in which a paper size, the number of copies, the paper direction (vertical/horizontal), a paper-supply unit and a paper-eject unit and the like is indicated in reverse-side printing, specially for continuing the printing operation without interruption when logical consistency in paper size, the number of copies and paper direction between the right and reverse sides is broken.
(3) A processing procedure on the detection of the following events:
(a) The number of sheets retained in the printer engine reaching a maximum limit. PA1 (b) The end of a document. PA1 (c) A change of paper size. PA1 (d) A change of paper-supply unit or paper-eject unit. PA1 (e) Circulation end of a sheet for first half printing.
In a printer with a circulation-type double-side printing mechanism as shown in FIGS. 3 and 4, first, the reverse (or right) side of a sheet is printed along a paper-supply path 1 and a paper-eject path 2 (first half printing), and second, the right (or reverse) side of the sheet is printed along a paper-supply path 2 and a paper-eject path 1 (second half printing). The "circulation end of the first half printing" is defined as a state in which sheets have been completed the first half printing and circulation within the printer engine, and the next second half printing through the paper-supply path 2 is allowed. (4) A multi-copy processing procedure for a case in which the number of copies is more than two, in particular, for a case in which the number of copies exceeds the maximum number of retained sheets in the printer engine.